Question

首先我从instructions查询

获取一些mysql

获取说明

function getAllInstructions(req,res){
    let mysqlQuery = `SELECT * FROM instructions where id = '` + req.params.id + "'";
    connection.query(mysqlQuery, function(err, rows, fields) {
    if (!err) {
        var instructions = new Array(); // <-- Getting my instructions there
        for (var i=0; i<rows.length;i++) {
             var instruction = new Instruction();
             instruction.id = rows[i].id;
             instruction.title = rows[i].title;
             instructions.push(instruction);
        }
    }
    else {
        console.log('Error while performing Query.');
    } 
});}

每条指令都有自己的steps。在我完成指令后，我需要为每条指令获得一个steps数组。

正在采取措施的功能

function getStepsForInstruction(_instructionId){
    let mysqlQuery = `SELECT * FROM steps where steps.instruction_id =  '` + _instructionId + "'";
    var steps = [];
    connection.query(mysqlQuery, function(err, rows, fields) {
    if (!err) {
        var steps = [];
        for (var i=0; i<rows.length; i++) {
            var step = new Step();
            step.id = rows[i].id;
            step.title = rows[i].title;
            steps.push(step);
        }
    }
    else {
        console.log('Error while performing Query.');
    }
});}

所以我想做这样的事情

for (var i=0;i<instructions.length;i++) {
     instructions[i].steps = getStepsForInstruction(instructions[i].id);
}

如何使用async或常见？

执行此操作

Answer 1

如果让getAllInstructions继续返回没有步骤的指令很重要，我会更改这些函数，以便它们返回promises（并使用正确的参数转义，以及其他一些小问题，如{ {1}}代替[]，new Array）：

Array#map

...然后使用function getAllInstructions(req, res) { return new Promise(function(resolve, reject) { connection.query('SELECT * FROM instructions where id = ?', [req.params.id], function(err, rows, fields) { if (err) { reject(err); } else { var instructions = rows.map(function(row) { var instruction = new Instruction(); instruction.id = row.id; instruction.title = row.title; return instruction; }); resolve(instructions); } }); }); } function getStepsForInstruction(_instructionId) { return new Promise(function(resolve, reject) { connection.query('SELECT * FROM steps where steps.instruction_id = ?', [_instructionId], function(err, rows, fields) { if (err) { reject(err); } else { var steps = rows.map(function(row) { var step = new Step(); step.id = row.id; step.title = row.title; return step; }); resolve(steps); } }); }); }：

Promise.all

但理想情况下，getAllInstructions(req, res).then(function(instructions) { return Promise.all(instructions.map(function(instruction) { return getStepsForInstruction(instruction.id).then(function(steps) { instruction.steps = steps; return instruction; }); }); }).then(function(instructions) { // They're all done, render them here });会填写我们的步骤，这简化了事情：

getAllInstructions

请注意，在上文中，我已手动处理为查询创建承诺，但是您可以使用库来实现＆＃34; promisify＆＃34;标准的Node风格的回调API，因此您不必手动完成。（搜索应该为此提供一些选项。）

一堆查询与动态参数

1 个答案: